This invention relates to an electromagnetic exhaust valve for use in metal casting and, more particularly, to an electromagnetic exhaust valve adapted to exhaust gas and air in the mold cavity in a metal mold used in metal casting and to press down molten metal rising above the mold cavity.
One example of a prior art metal casting apparatus will firstly be described with reference to FIG. 2 of the accompanying drawings.
As shown, a stationary metal mold 12 is secured to the upper surface of a stationary die plate 11, while a movable metal mold 13 opposing the stationary metal mold 12 is secured to the lower surface of a movable die plate 14. When mated together, the stationary and movable metal molds 12 and 13 define therebetween a mold cavity 15. A crucible 17 containing molten metal 16 is secured to the lower surface of the stationary die plate 11. The molten metal 16 is filled into the cavity 15 through a stalk 18 secured to the stationary die plate 11 by applying compressed air on the upper surface of the molten metal from a source of pressurized gas 50 as shown by arrows.
For the purpose of exhausting to the outside gas and air existing in the cavity 15 at the time of filling the molten metal into the cavity, exhaust plugs 20 are provided between a cavity 15 and a chamber 19 communicated with the atmosphere. An ejector 21 is provided in the chamber 19 for ejecting a casting out of the cavity 15. More particularly, after casting a product, as the movable die plate 14 is retracted upwardly, the casting too is moved upwardly together with the movable metal mold 13. At this time, the ejector 21 is moved downwardly by a push rod, not shown, to cause the casting to drop.
As diagrammatically shown in FIGS. 3 and 4, each exhaust plug 20 has a tubular configuration 26 provided with a plurality of axial grooves 27 on the peripheral surface or a plurality of axial openings 28. Alternatively, a body 26 of sintered metal powder, shown in FIG. 5, is used. For the purpose of permitting the plugs 20 to discharge gas or air but preventing the plugs from passing the molten metal, the sizes of grooves 27 and openings 28 are made small, for example about 0.2 mm. Accordingly, not only the exhausting efficiency is small but also a long time is necessary for effecting sufficient exhaustion, thus decreasing the productivity. Sometimes, the quantity of the filled molten metal becomes deficient, resulting in rejects. If the cross-sectional areas of the grooves 27 and openings 28 were too large, the molten metal would enter into these grooves or openings and solidify therein. Such clogged plugs cannot be used again.